The invention relates to an operating mechanism for valves and the like, having a housing, a port situated in the housing, which is to be opened or closed by a valve plate, and a seat associated with the port, in which the turning of a shaft in the one direction produces a movement of the valve plate from its open position to its closed position, and thereafter a pressing movement of the valve plate against the seat, and in which a turning of the shaft in the other direction produces movement of the valve plate in the reverse direction.
In operating mechanisms of this kind (cf., for example, the pendulum valve of GB-PS No. 1,050,435) it is important that the valve plate perform no additional lateral movements during the movement by which it is pressed perpendicularly against the valve seat, so that the often very delicate sealing surfaces will not exercise a rubbing action against one another. It is furthermore important that the pressing movement will not be initiated during the movement of the valve plate from its open position to its closed position, thereby producing likewise undesirable friction with the housing. To permit the achievement of such movements of a valve plate with only one rotatory movement of an operating shaft, it is known to provide two levers on the shaft, one of which is temporarily at rest during the turning of the operating shaft, as a result of engaging ratchet mechanisms. Such ratchet mechanisms have a relatively large number of parts moving relatively to one another, including tension or compression springs, whose operation is not absolutely reliable, especially after relatively long use. In the case of formerly known valves of this kind, it can therefore happen that the valve plate will come into contact with housing parts due to premature initiation of the pressing movement, resulting in damage to the sealing surfaces, so that the tightness of the seals deteriorates. Premature contact between the valve plate and the housing can even result in seizure, so that they can no longer be brought completely into the closed position.